12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I39 



Table 2. — Ontogeny 



Average No. 



diaphragms Width of 



in mesopores exozone Axial ratio 



2 O.3-O.6 O.87-O.92 



3 0.5-1.0 O.74-O.9O 



Frag. A. lectotype 4 1-2 0.82 



4 0.9-1.4 0.71-0.86 



5 1. 0-1.4 0.66-0.82 



6 1.4-I.8 0.75 

 Frag. B. lectotype 7 i-6 0.67 



7 1.1-1.6 0.68-0.70 



DISCUSSION 



The number of mesopore diaphragms and the width of the exozone 

 are not particularly sensitive indicators for ontogenetic development of 

 the mesopores and zooecia in T. tuberculosa. The variation in dia- 

 phragm counts and in width of exozone within a longitudinal thin sec- 

 tion is unusually large because of a marked variation in the number 

 of chambers developed in adjacent mesopores in the inner region. 

 Also, the unusual variation in thickness and spacing of mesopore dia- 

 phragms in the outer region of the exozone makes diaphragm counts 

 less reliable. 



T. tuberculosa differs from both T. halli and T. whitfieldi in having 

 the larger branches, tuberculated mesopores, and a broader exozone in 

 mature specimens. Both T. halli and T. whitfieldi are smooth, 

 rhomboporoid-sized species. 



REFERENCES 

 Bassler, R. S. 



1906. The bryozoan fauna of the Rochester shale. U. S. Geol. Surv. Bull. 



No. 292, 65 pp., 31 pis. 

 191 1. The early Paleozoic Bryozoa of the Baltic Provinces. U. S. Nat. 

 Mus. Bull. 77, 348 pp., 13 pis. 



BOARDMAN, R. S. 



Trepostomatous Bryozoa of the Hamilton group of New York State. 

 U. S. Geol. Surv. Prof. Pap. 340, in press. 

 Cumings, E. R., and Galloway, J. J. 



1915. Studies of the morphology and histology of the Trepostomata or 

 monticuliporoids. Bull. Geol. Soc. Amer., vol. 26, pp. 349-374, pis. 

 10-15. 

 Hall, James. 



1851. In Silliman, B., Silliman, B., Jr., and Dana, J. D., eds. New genera of 

 fossil corals from the report by James Hall on the Paleontology 

 of New York. Amer. Journ. Sci. and Arts, ser. 2, vol. n, pp. 

 398-401. 



